broken pins

I am still working on my very first own PCB. I got it populated and it almost works. That is everything but 3 pins. The pins seem to be completely dead. That is the issue is not that the traces or connections are bead. Even if I measure them directly at the CPU they do not react on anything I code.

I always thought AVRs have very good ESD proection. None of the DIP parts ever had something like this even with careless handling. But my first SMD part (Atmega 644P) has 3 broken pins? The pins are not adjacent. Has anyone an idea how something like this might happen?

Udo

If it is an SMD part, there could be a lot of reasons. I would look very carefully at the pins with a magnifying glass or loup and make sure there are no solder bridges shorting them out. Also double check that they are actually soldered to the board.

Heat damage from soldering may have done something too.

It may be just coincidence, but I have had four smd Arduinos stop working properly for no obvious reason after they have been in service for a few weeks. They could have intermittent oscillators because they all stop & start at random but I have not had a chance to check with a scope yet.
The dip versions are all still going strong with no failures at all.

I’ve worked with a bunch of SMD Atmega2560’s and never had a problem… and those have a 100 pins. Are you using filter caps at the power pins? and on the regulator if you have one? and a pullup resistor on the reset?

Which pins?

Without a series resistance the protection diodes do not provide a lot of protection.
I know the reset pin does not have a protection diode. I am not
sure if there are any other pins without a diode.

(* jcl *)

Broken pins:

PORTC, Pin 2 and 3
PORTD, Pin 7

And yes: I have 100nF at each power pin and filter caps before and behind the regulator as described in the regulator’s datasheet. The whole circuit works. The processor is running and my st7565 display shows proper content. Only these 3 pins won’t behave.

Udo